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Filename :
synchronization.py
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"""Synchronization functions. File- and mutex-based mutual exclusion synchronizers are provided, as well as a name-based mutex which locks within an application based on a string name. """ import os import sys import tempfile try: import threading as _threading except ImportError: import dummy_threading as _threading # check for fcntl module try: sys.getwindowsversion() has_flock = False except: try: import fcntl has_flock = True except ImportError: has_flock = False from beaker import util from beaker.exceptions import LockError __all__ = ["file_synchronizer", "mutex_synchronizer", "null_synchronizer", "NameLock", "_threading"] class NameLock(object): """a proxy for an RLock object that is stored in a name based registry. Multiple threads can get a reference to the same RLock based on the name alone, and synchronize operations related to that name. """ locks = util.WeakValuedRegistry() class NLContainer(object): def __init__(self, reentrant): if reentrant: self.lock = _threading.RLock() else: self.lock = _threading.Lock() def __call__(self): return self.lock def __init__(self, identifier = None, reentrant = False): if identifier is None: self._lock = NameLock.NLContainer(reentrant) else: self._lock = NameLock.locks.get(identifier, NameLock.NLContainer, reentrant) def acquire(self, wait = True): return self._lock().acquire(wait) def release(self): self._lock().release() _synchronizers = util.WeakValuedRegistry() def _synchronizer(identifier, cls, **kwargs): return _synchronizers.sync_get((identifier, cls), cls, identifier, **kwargs) def file_synchronizer(identifier, **kwargs): if not has_flock or 'lock_dir' not in kwargs: return mutex_synchronizer(identifier) else: return _synchronizer(identifier, FileSynchronizer, **kwargs) def mutex_synchronizer(identifier, **kwargs): return _synchronizer(identifier, ConditionSynchronizer, **kwargs) class null_synchronizer(object): def acquire_write_lock(self, wait=True): return True def acquire_read_lock(self): pass def release_write_lock(self): pass def release_read_lock(self): pass acquire = acquire_write_lock release = release_write_lock class SynchronizerImpl(object): def __init__(self): self._state = util.ThreadLocal() class SyncState(object): __slots__ = 'reentrantcount', 'writing', 'reading' def __init__(self): self.reentrantcount = 0 self.writing = False self.reading = False def state(self): if not self._state.has(): state = SynchronizerImpl.SyncState() self._state.put(state) return state else: return self._state.get() state = property(state) def release_read_lock(self): state = self.state if state.writing: raise LockError("lock is in writing state") if not state.reading: raise LockError("lock is not in reading state") if state.reentrantcount == 1: self.do_release_read_lock() state.reading = False state.reentrantcount -= 1 def acquire_read_lock(self, wait = True): state = self.state if state.writing: raise LockError("lock is in writing state") if state.reentrantcount == 0: x = self.do_acquire_read_lock(wait) if (wait or x): state.reentrantcount += 1 state.reading = True return x elif state.reading: state.reentrantcount += 1 return True def release_write_lock(self): state = self.state if state.reading: raise LockError("lock is in reading state") if not state.writing: raise LockError("lock is not in writing state") if state.reentrantcount == 1: self.do_release_write_lock() state.writing = False state.reentrantcount -= 1 release = release_write_lock def acquire_write_lock(self, wait = True): state = self.state if state.reading: raise LockError("lock is in reading state") if state.reentrantcount == 0: x = self.do_acquire_write_lock(wait) if (wait or x): state.reentrantcount += 1 state.writing = True return x elif state.writing: state.reentrantcount += 1 return True acquire = acquire_write_lock def do_release_read_lock(self): raise NotImplementedError() def do_acquire_read_lock(self): raise NotImplementedError() def do_release_write_lock(self): raise NotImplementedError() def do_acquire_write_lock(self): raise NotImplementedError() class FileSynchronizer(SynchronizerImpl): """a synchronizer which locks using flock(). Adapted for Python/multithreads from Apache::Session::Lock::File, http://search.cpan.org/src/CWEST/Apache-Session-1.81/Session/Lock/File.pm This module does not unlink temporary files, because it interferes with proper locking. This can cause problems on certain systems (Linux) whose file systems (ext2) do not perform well with lots of files in one directory. To prevent this you should use a script to clean out old files from your lock directory. """ def __init__(self, identifier, lock_dir): super(FileSynchronizer, self).__init__() self._filedescriptor = util.ThreadLocal() if lock_dir is None: lock_dir = tempfile.gettempdir() else: lock_dir = lock_dir self.filename = util.encoded_path( lock_dir, [identifier], extension='.lock' ) def _filedesc(self): return self._filedescriptor.get() _filedesc = property(_filedesc) def _open(self, mode): filedescriptor = self._filedesc if filedescriptor is None: filedescriptor = os.open(self.filename, mode) self._filedescriptor.put(filedescriptor) return filedescriptor def do_acquire_read_lock(self, wait): filedescriptor = self._open(os.O_CREAT | os.O_RDONLY) if not wait: try: fcntl.flock(filedescriptor, fcntl.LOCK_SH | fcntl.LOCK_NB) return True except IOError: os.close(filedescriptor) self._filedescriptor.remove() return False else: fcntl.flock(filedescriptor, fcntl.LOCK_SH) return True def do_acquire_write_lock(self, wait): filedescriptor = self._open(os.O_CREAT | os.O_WRONLY) if not wait: try: fcntl.flock(filedescriptor, fcntl.LOCK_EX | fcntl.LOCK_NB) return True except IOError: os.close(filedescriptor) self._filedescriptor.remove() return False else: fcntl.flock(filedescriptor, fcntl.LOCK_EX) return True def do_release_read_lock(self): self._release_all_locks() def do_release_write_lock(self): self._release_all_locks() def _release_all_locks(self): filedescriptor = self._filedesc if filedescriptor is not None: fcntl.flock(filedescriptor, fcntl.LOCK_UN) os.close(filedescriptor) self._filedescriptor.remove() class ConditionSynchronizer(SynchronizerImpl): """a synchronizer using a Condition.""" def __init__(self, identifier): super(ConditionSynchronizer, self).__init__() # counts how many asynchronous methods are executing self.async = 0 # pointer to thread that is the current sync operation self.current_sync_operation = None # condition object to lock on self.condition = _threading.Condition(_threading.Lock()) def do_acquire_read_lock(self, wait = True): self.condition.acquire() try: # see if a synchronous operation is waiting to start # or is already running, in which case we wait (or just # give up and return) if wait: while self.current_sync_operation is not None: self.condition.wait() else: if self.current_sync_operation is not None: return False self.async += 1 finally: self.condition.release() if not wait: return True def do_release_read_lock(self): self.condition.acquire() try: self.async -= 1 # check if we are the last asynchronous reader thread # out the door. if self.async == 0: # yes. so if a sync operation is waiting, notifyAll to wake # it up if self.current_sync_operation is not None: self.condition.notifyAll() elif self.async < 0: raise LockError("Synchronizer error - too many " "release_read_locks called") finally: self.condition.release() def do_acquire_write_lock(self, wait = True): self.condition.acquire() try: # here, we are not a synchronous reader, and after returning, # assuming waiting or immediate availability, we will be. if wait: # if another sync is working, wait while self.current_sync_operation is not None: self.condition.wait() else: # if another sync is working, # we dont want to wait, so forget it if self.current_sync_operation is not None: return False # establish ourselves as the current sync # this indicates to other read/write operations # that they should wait until this is None again self.current_sync_operation = _threading.currentThread() # now wait again for asyncs to finish if self.async > 0: if wait: # wait self.condition.wait() else: # we dont want to wait, so forget it self.current_sync_operation = None return False finally: self.condition.release() if not wait: return True def do_release_write_lock(self): self.condition.acquire() try: if self.current_sync_operation is not _threading.currentThread(): raise LockError("Synchronizer error - current thread doesnt " "have the write lock") # reset the current sync operation so # another can get it self.current_sync_operation = None # tell everyone to get ready self.condition.notifyAll() finally: # everyone go !! self.condition.release()